INTRODUCTION 13 



That there is great diversity in the marine coast 

 floras of different regions is well known, and a 

 comparison of three remote and dissimilar regions 

 furnishes an extreme case. It would be difficult to 

 select three instances of less geographical relation- 

 ship than the Arctic Sea, the West Indies, and 

 Australia. The first has 259 species in 111 genera, 

 the second 788 species in 150 genera, and the third 

 has 1,132 species in 255 genera. The Arctic Sea 

 has 42 genera and 30 species in common with the 

 West Indies, the same number of genera and 21 

 species in common with Australia, while out of the 

 two larger totals from the West Indies and Australia 

 there are 109 genera and 135 species in common. 

 If we take the forms common to all three there are 

 32 generic types, but only 12 species out of these 

 large totals sufficiently cosmopolitan to occur so 

 widely. An analysis of the totals shows that in the 

 Arctic regions the genus averages slightly more than 

 2 species only, while in the West Indies it is rather 

 more than 5, and on Australian coasts rather less. The 

 north temperate Atlantic yields an average of about 

 4J species to the genus, while the South African 

 coast gives us only 3, a result which may be attributed 

 to its small coast-line. There is still a great lack of 

 material on which to found such comparisons with 

 many regions of the ocean, and in the absence of full 

 records the making of contrasts is only misleading. 

 Enough has been said to show the diversity of such 

 floras, the means of distribution, and the principal 

 natural barriers that delimit the boundaries of areas. 



A comparison of the Arctic and the Antarctic 



